#ifndef SECP256K1_H
#define SECP256K1_H

#ifdef __cplusplus
extern "C" {
#endif

#include <stddef.h>


    /* These rules specify the order of arguments in API calls:
     *
     * 1. Context pointers go first, followed by output arguments, combined
     *    output/input arguments, and finally input-only arguments.
     * 2. Array lengths always immediately the follow the argument whose length
     *    they describe, even if this violates rule 1.
     * 3. Within the OUT/OUTIN/IN groups, pointers to data that is typically generated
     *    later go first. This means: signatures, public nonces, secret nonces,
     *    messages, public keys, secret keys, tweaks.
     * 4. Arguments that are not data pointers go last, from more complex to less
     *    complex: function pointers, algorithm names, messages, void pointers,
     *    counts, flags, booleans.
     * 5. Opaque data pointers follow the function pointer they are to be passed to.
     */

     /** Opaque data structure that holds context information (precomputed tables etc.).
      *
      *  The purpose of context structures is to cache large precomputed data tables
      *  that are expensive to construct, and also to maintain the randomization data
      *  for blinding.
      *
      *  Do not create a new context object for each operation, as construction is
      *  far slower than all other API calls (~100 times slower than an ECDSA
      *  verification).
      *
      *  A constructed context can safely be used from multiple threads
      *  simultaneously, but API calls that take a non-const pointer to a context
      *  need exclusive access to it. In particular this is the case for
      *  rustsecp256k1_v0_4_0_context_destroy, rustsecp256k1_v0_4_0_context_preallocated_destroy,
      *  and rustsecp256k1_v0_4_0_context_randomize.
      *
      *  Regarding randomization, either do it once at creation time (in which case
      *  you do not need any locking for the other calls), or use a read-write lock.
      */
    typedef struct rustsecp256k1_v0_4_0_context_struct rustsecp256k1_v0_4_0_context;

    //struct rustsecp256k1_v0_4_0_context_struct {
    //    rustsecp256k1_v0_4_0_ecmult_context ecmult_ctx;
    //    rustsecp256k1_v0_4_0_ecmult_gen_context ecmult_gen_ctx;
    //    rustsecp256k1_v0_4_0_callback illegal_callback;
    //    rustsecp256k1_v0_4_0_callback error_callback;
    //    int declassify;
    //};

    /** Opaque data structure that holds rewriteable "scratch space"
     *
     *  The purpose of this structure is to replace dynamic memory allocations,
     *  because we target architectures where this may not be available. It is
     *  essentially a resizable (within specified parameters) block of bytes,
     *  which is initially created either by memory allocation or TODO as a pointer
     *  into some fixed rewritable space.
     *
     *  Unlike the context object, this cannot safely be shared between threads
     *  without additional synchronization logic.
     */
    typedef struct rustsecp256k1_v0_4_0_scratch_space_struct rustsecp256k1_v0_4_0_scratch_space;

    /** Opaque data structure that holds a parsed and valid public key.
     *
     *  The exact representation of data inside is implementation defined and not
     *  guaranteed to be portable between different platforms or versions. It is
     *  however guaranteed to be 64 bytes in size, and can be safely copied/moved.
     *  If you need to convert to a format suitable for storage, transmission, or
     *  comparison, use rustsecp256k1_v0_4_0_ec_pubkey_serialize and rustsecp256k1_v0_4_0_ec_pubkey_parse.
     */
    typedef struct {
        unsigned char data[64];
    } rustsecp256k1_v0_4_0_pubkey;

    /** Opaque data structured that holds a parsed ECDSA signature.
     *
     *  The exact representation of data inside is implementation defined and not
     *  guaranteed to be portable between different platforms or versions. It is
     *  however guaranteed to be 64 bytes in size, and can be safely copied/moved.
     *  If you need to convert to a format suitable for storage, transmission, or
     *  comparison, use the rustsecp256k1_v0_4_0_ecdsa_signature_serialize_* and
     *  rustsecp256k1_v0_4_0_ecdsa_signature_parse_* functions.
     */
    typedef struct {
        unsigned char data[64];
    } rustsecp256k1_v0_4_0_ecdsa_signature;

    /** A pointer to a function to deterministically generate a nonce.
     *
     * Returns: 1 if a nonce was successfully generated. 0 will cause signing to fail.
     * Out:     nonce32:   pointer to a 32-byte array to be filled by the function.
     * In:      msg32:     the 32-byte message hash being verified (will not be NULL)
     *          key32:     pointer to a 32-byte secret key (will not be NULL)
     *          algo16:    pointer to a 16-byte array describing the signature
     *                     algorithm (will be NULL for ECDSA for compatibility).
     *          data:      Arbitrary data pointer that is passed through.
     *          attempt:   how many iterations we have tried to find a nonce.
     *                     This will almost always be 0, but different attempt values
     *                     are required to result in a different nonce.
     *
     * Except for test cases, this function should compute some cryptographic hash of
     * the message, the algorithm, the key and the attempt.
     */
    typedef int (*rustsecp256k1_v0_4_0_nonce_function)(
        unsigned char* nonce32,
        const unsigned char* msg32,
        const unsigned char* key32,
        const unsigned char* algo16,
        void* data,
        unsigned int attempt
        );

# if !defined(SECP256K1_GNUC_PREREQ)
#  if defined(__GNUC__)&&defined(__GNUC_MINOR__)
#   define SECP256K1_GNUC_PREREQ(_maj,_min) \
 ((__GNUC__<<16)+__GNUC_MINOR__>=((_maj)<<16)+(_min))
#  else
#   define SECP256K1_GNUC_PREREQ(_maj,_min) 0
#  endif
# endif

# if (!defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L) )
#  if SECP256K1_GNUC_PREREQ(2,7)
#   define SECP256K1_INLINE __inline__
#  elif (defined(_MSC_VER))
#   define SECP256K1_INLINE __inline
#  else
#   define SECP256K1_INLINE
#  endif
# else
#  define SECP256K1_INLINE inline
# endif

#ifndef SECP256K1_API
# if defined(_WIN32)
#  ifdef SECP256K1_BUILD
#   define SECP256K1_API __declspec(dllexport)
#  else
#   define SECP256K1_API
#  endif
# elif defined(__GNUC__) && (__GNUC__ >= 4) && defined(SECP256K1_BUILD)
#  define SECP256K1_API __attribute__ ((visibility ("default")))
# else
#  define SECP256K1_API
# endif
#endif

    /**Warning attributes
      * NONNULL is not used if SECP256K1_BUILD is set to avoid the compiler optimizing out
      * some paranoid null checks. */
# if defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
#  define SECP256K1_WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
# else
#  define SECP256K1_WARN_UNUSED_RESULT
# endif
# if !defined(SECP256K1_BUILD) && defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
#  define SECP256K1_ARG_NONNULL(_x)  __attribute__ ((__nonnull__(_x)))
# else
#  define SECP256K1_ARG_NONNULL(_x)
# endif

      /** All flags' lower 8 bits indicate what they're for. Do not use directly. */
#define SECP256K1_FLAGS_TYPE_MASK ((1 << 8) - 1)
#define SECP256K1_FLAGS_TYPE_CONTEXT (1 << 0)
#define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
/** The higher bits contain the actual data. Do not use directly. */
#define SECP256K1_FLAGS_BIT_CONTEXT_VERIFY (1 << 8)
#define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9)
#define SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY (1 << 10)
#define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)

/** Flags to pass to rustsecp256k1_v0_4_0_context_create, rustsecp256k1_v0_4_0_context_preallocated_size, and
 *  rustsecp256k1_v0_4_0_context_preallocated_create. */
#define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY)
#define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN)
#define SECP256K1_CONTEXT_DECLASSIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY)
#define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)

 /** Flag to pass to rustsecp256k1_v0_4_0_ec_pubkey_serialize. */
#define SECP256K1_EC_COMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION | SECP256K1_FLAGS_BIT_COMPRESSION)
#define SECP256K1_EC_UNCOMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION)

/** Prefix byte used to tag various encoded curvepoints for specific purposes */
#define SECP256K1_TAG_PUBKEY_EVEN 0x02
#define SECP256K1_TAG_PUBKEY_ODD 0x03
#define SECP256K1_TAG_PUBKEY_UNCOMPRESSED 0x04
#define SECP256K1_TAG_PUBKEY_HYBRID_EVEN 0x06
#define SECP256K1_TAG_PUBKEY_HYBRID_ODD 0x07

/** A simple secp256k1 context object with no precomputed tables. These are useful for
 *  type serialization/parsing functions which require a context object to maintain
 *  API consistency, but currently do not require expensive precomputations or dynamic
 *  allocations.
 */
    SECP256K1_API extern const rustsecp256k1_v0_4_0_context* rustsecp256k1_v0_4_0_context_no_precomp;

    /** Create a secp256k1 context object (in dynamically allocated memory).
     *
     *  This function uses malloc to allocate memory. It is guaranteed that malloc is
     *  called at most once for every call of this function. If you need to avoid dynamic
     *  memory allocation entirely, see the functions in rustsecp256k1_v0_4_0_preallocated.h.
     *
     *  Returns: a newly created context object.
     *  In:      flags: which parts of the context to initialize.
     *
     *  See also rustsecp256k1_v0_4_0_context_randomize.
     */
    SECP256K1_API rustsecp256k1_v0_4_0_context* rustsecp256k1_v0_4_0_context_create(
        unsigned int flags
    ) SECP256K1_WARN_UNUSED_RESULT;

     /** Copy a secp256k1 context object (into dynamically allocated memory).
      *
      *  This function uses malloc to allocate memory. It is guaranteed that malloc is
      *  called at most once for every call of this function. If you need to avoid dynamic
      *  memory allocation entirely, see the functions in rustsecp256k1_v0_4_0_preallocated.h.
      *
      *  Returns: a newly created context object.
      *  Args:    ctx: an existing context to copy (cannot be NULL)
      */
    SECP256K1_API rustsecp256k1_v0_4_0_context* rustsecp256k1_v0_4_0_context_clone(
        const rustsecp256k1_v0_4_0_context* ctx
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT;

      /** Destroy a secp256k1 context object (created in dynamically allocated memory).
       *
       *  The context pointer may not be used afterwards.
       *
       *  The context to destroy must have been created using rustsecp256k1_v0_4_0_context_create
       *  or rustsecp256k1_v0_4_0_context_clone. If the context has instead been created using
       *  rustsecp256k1_v0_4_0_context_preallocated_create or rustsecp256k1_v0_4_0_context_preallocated_clone, the
       *  behaviour is undefined. In that case, rustsecp256k1_v0_4_0_context_preallocated_destroy must
       *  be used instead.
       *
       *  Args:   ctx: an existing context to destroy, constructed using
       *               rustsecp256k1_v0_4_0_context_create or rustsecp256k1_v0_4_0_context_clone
       */
    SECP256K1_API void rustsecp256k1_v0_4_0_context_destroy(
        rustsecp256k1_v0_4_0_context* ctx
    );

       /** Set a callback function to be called when an illegal argument is passed to
        *  an API call. It will only trigger for violations that are mentioned
        *  explicitly in the header.
        *
        *  The philosophy is that these shouldn't be dealt with through a
        *  specific return value, as calling code should not have branches to deal with
        *  the case that this code itself is broken.
        *
        *  On the other hand, during debug stage, one would want to be informed about
        *  such mistakes, and the default (crashing) may be inadvisable.
        *  When this callback is triggered, the API function called is guaranteed not
        *  to cause a crash, though its return value and output arguments are
        *  undefined.
        *
        *  When this function has not been called (or called with fn==NULL), then the
        *  default handler will be used. The library provides a default handler which
        *  writes the message to stderr and calls abort. This default handler can be
        *  replaced at link time if the preprocessor macro
        *  USE_EXTERNAL_DEFAULT_CALLBACKS is defined, which is the case if the build
        *  has been configured with --enable-external-default-callbacks. Then the
        *  following two symbols must be provided to link against:
        *   - void rustsecp256k1_v0_4_0_default_illegal_callback_fn(const char* message, void* data);
        *   - void rustsecp256k1_v0_4_0_default_error_callback_fn(const char* message, void* data);
        *  The library can call these default handlers even before a proper callback data
        *  pointer could have been set using rustsecp256k1_v0_4_0_context_set_illegal_callback or
        *  rustsecp256k1_v0_4_0_context_set_error_callback, e.g., when the creation of a context
        *  fails. In this case, the corresponding default handler will be called with
        *  the data pointer argument set to NULL.
        *
        *  Args: ctx:  an existing context object (cannot be NULL)
        *  In:   fun:  a pointer to a function to call when an illegal argument is
        *              passed to the API, taking a message and an opaque pointer.
        *              (NULL restores the default handler.)
        *        data: the opaque pointer to pass to fun above.
        *
        *  See also rustsecp256k1_v0_4_0_context_set_error_callback.
        */
    SECP256K1_API void rustsecp256k1_v0_4_0_context_set_illegal_callback(
        rustsecp256k1_v0_4_0_context* ctx,
        void (*fun)(const char* message, void* data),
        const void* data
    ) SECP256K1_ARG_NONNULL(1);

    /** Set a callback function to be called when an internal consistency check
     *  fails. The default is crashing.
     *rustsecp256k1_v0_4_0_context_create
     *  This can only trigger in case of a hardware failure, miscompilation,
     *  memory corruption, serious bug in the library, or other error would can
     *  otherwise result in undefined behaviour. It will not trigger due to mere
     *  incorrect usage of the API (see rustsecp256k1_v0_4_0_context_set_illegal_callback
     *  for that). After this callback returns, anything may happen, including
     *  crashing.
     *
     *  Args: ctx:  an existing context object (cannot be NULL)
     *  In:   fun:  a pointer to a function to call when an internal error occurs,
     *              taking a message and an opaque pointer (NULL restores the
     *              default handler, see rustsecp256k1_v0_4_0_context_set_illegal_callback
     *              for details).
     *        data: the opaque pointer to pass to fun above.
     *
     *  See also rustsecp256k1_v0_4_0_context_set_illegal_callback.
     */
    SECP256K1_API void rustsecp256k1_v0_4_0_context_set_error_callback(
        rustsecp256k1_v0_4_0_context* ctx,
        void (*fun)(const char* message, void* data),
        const void* data
    ) SECP256K1_ARG_NONNULL(1);

    /** Create a secp256k1 scratch space object.
     *
     *  Returns: a newly created scratch space.
     *  Args: ctx:  an existing context object (cannot be NULL)
     *  In:   size: amount of memory to be available as scratch space. Some extra
     *              (<100 bytes) will be allocated for extra accounting.
     */

     /** Destroy a secp256k1 scratch space.
      *
      *  The pointer may not be used afterwards.
      *  Args:       ctx: a secp256k1 context object.
      *          scratch: space to destroy
      */

      /** Parse a variable-length public key into the pubkey object.
       *
       *  Returns: 1 if the public key was fully valid.
       *           0 if the public key could not be parsed or is invalid.
       *  Args: ctx:      a secp256k1 context object.
       *  Out:  pubkey:   pointer to a pubkey object. If 1 is returned, it is set to a
       *                  parsed version of input. If not, its value is undefined.
       *  In:   input:    pointer to a serialized public key
       *        inputlen: length of the array pointed to by input
       *
       *  This function supports parsing compressed (33 bytes, header byte 0x02 or
       *  0x03), uncompressed (65 bytes, header byte 0x04), or hybrid (65 bytes, header
       *  byte 0x06 or 0x07) format public keys.
       */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_pubkey_parse(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_pubkey* pubkey,
        const unsigned char* input,
        size_t inputlen
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Serialize a pubkey object into a serialized byte sequence.
     *
     *  Returns: 1 always.
     *  Args:   ctx:        a secp256k1 context object.
     *  Out:    output:     a pointer to a 65-byte (if compressed==0) or 33-byte (if
     *                      compressed==1) byte array to place the serialized key
     *                      in.
     *  In/Out: outputlen:  a pointer to an integer which is initially set to the
     *                      size of output, and is overwritten with the written
     *                      size.
     *  In:     pubkey:     a pointer to a rustsecp256k1_v0_4_0_pubkey containing an
     *                      initialized public key.
     *          flags:      SECP256K1_EC_COMPRESSED if serialization should be in
     *                      compressed format, otherwise SECP256K1_EC_UNCOMPRESSED.
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ec_pubkey_serialize(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* output,
        size_t* outputlen,
        const rustsecp256k1_v0_4_0_pubkey* pubkey,
        unsigned int flags
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

    /** Parse an ECDSA signature in compact (64 bytes) format.
     *
     *  Returns: 1 when the signature could be parsed, 0 otherwise.
     *  Args: ctx:      a secp256k1 context object
     *  Out:  sig:      a pointer to a signature object
     *  In:   input64:  a pointer to the 64-byte array to parse
     *
     *  The signature must consist of a 32-byte big endian R value, followed by a
     *  32-byte big endian S value. If R or S fall outside of [0..order-1], the
     *  encoding is invalid. R and S with value 0 are allowed in the encoding.
     *
     *  After the call, sig will always be initialized. If parsing failed or R or
     *  S are zero, the resulting sig value is guaranteed to fail validation for any
     *  message and public key.
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ecdsa_signature_parse_compact(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_ecdsa_signature* sig,
        const unsigned char* input64
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Parse a DER ECDSA signature.
     *
     *  Returns: 1 when the signature could be parsed, 0 otherwise.
     *  Args: ctx:      a secp256k1 context object
     *  Out:  sig:      a pointer to a signature object
     *  In:   input:    a pointer to the signature to be parsed
     *        inputlen: the length of the array pointed to be input
     *
     *  This function will accept any valid DER encoded signature, even if the
     *  encoded numbers are out of range.
     *
     *  After the call, sig will always be initialized. If parsing failed or the
     *  encoded numbers are out of range, signature validation with it is
     *  guaranteed to fail for every message and public key.
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ecdsa_signature_parse_der(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_ecdsa_signature* sig,
        const unsigned char* input,
        size_t inputlen
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Serialize an ECDSA signature in DER format.
     *
     *  Returns: 1 if enough space was available to serialize, 0 otherwise
     *  Args:   ctx:       a secp256k1 context object
     *  Out:    output:    a pointer to an array to store the DER serialization
     *  In/Out: outputlen: a pointer to a length integer. Initially, this integer
     *                     should be set to the length of output. After the call
     *                     it will be set to the length of the serialization (even
     *                     if 0 was returned).
     *  In:     sig:       a pointer to an initialized signature object
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ecdsa_signature_serialize_der(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* output,
        size_t* outputlen,
        const rustsecp256k1_v0_4_0_ecdsa_signature* sig
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

    /** Serialize an ECDSA signature in compact (64 byte) format.
     *
     *  Returns: 1
     *  Args:   ctx:       a secp256k1 context object
     *  Out:    output64:  a pointer to a 64-byte array to store the compact serialization
     *  In:     sig:       a pointer to an initialized signature object
     *
     *  See rustsecp256k1_v0_4_0_ecdsa_signature_parse_compact for details about the encoding.
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ecdsa_signature_serialize_compact(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* output64,
        const rustsecp256k1_v0_4_0_ecdsa_signature* sig
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Verify an ECDSA signature.
     *
     *  Returns: 1: correct signature
     *           0: incorrect or unparseable signature
     *  Args:    ctx:       a secp256k1 context object, initialized for verification.
     *  In:      sig:       the signature being verified (cannot be NULL)
     *           msghash32: the 32-byte message hash being verified (cannot be NULL).
     *                      The verifier must make sure to apply a cryptographic
     *                      hash function to the message by itself and not accept an
     *                      msghash32 value directly. Otherwise, it would be easy to
     *                      create a "valid" signature without knowledge of the
     *                      secret key. See also
     *                      https://bitcoin.stackexchange.com/a/81116/35586 for more
     *                      background on this topic.
     *           pubkey:    pointer to an initialized public key to verify with (cannot be NULL)
     *
     * To avoid accepting malleable signatures, only ECDSA signatures in lower-S
     * form are accepted.
     *
     * If you need to accept ECDSA signatures from sources that do not obey this
     * rule, apply rustsecp256k1_v0_4_0_ecdsa_signature_normalize to the signature prior to
     * validation, but be aware that doing so results in malleable signatures.
     *
     * For details, see the comments for that function.
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ecdsa_verify(
        const rustsecp256k1_v0_4_0_context* ctx,
        const rustsecp256k1_v0_4_0_ecdsa_signature* sig,
        const unsigned char* msghash32,
        const rustsecp256k1_v0_4_0_pubkey* pubkey
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

    /** Convert a signature to a normalized lower-S form.
     *
     *  Returns: 1 if sigin was not normalized, 0 if it already was.
     *  Args: ctx:    a secp256k1 context object
     *  Out:  sigout: a pointer to a signature to fill with the normalized form,
     *                or copy if the input was already normalized. (can be NULL if
     *                you're only interested in whether the input was already
     *                normalized).
     *  In:   sigin:  a pointer to a signature to check/normalize (cannot be NULL,
     *                can be identical to sigout)
     *
     *  With ECDSA a third-party can forge a second distinct signature of the same
     *  message, given a single initial signature, but without knowing the key. This
     *  is done by negating the S value modulo the order of the curve, 'flipping'
     *  the sign of the random point R which is not included in the signature.
     *
     *  Forgery of the same message isn't universally problematic, but in systems
     *  where message malleability or uniqueness of signatures is important this can
     *  cause issues. This forgery can be blocked by all verifiers forcing signers
     *  to use a normalized form.
     *
     *  The lower-S form reduces the size of signatures slightly on average when
     *  variable length encodings (such as DER) are used and is cheap to verify,
     *  making it a good choice. Security of always using lower-S is assured because
     *  anyone can trivially modify a signature after the fact to enforce this
     *  property anyway.
     *
     *  The lower S value is always between 0x1 and
     *  0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0,
     *  inclusive.
     *
     *  No other forms of ECDSA malleability are known and none seem likely, but
     *  there is no formal proof that ECDSA, even with this additional restriction,
     *  is free of other malleability. Commonly used serialization schemes will also
     *  accept various non-unique encodings, so care should be taken when this
     *  property is required for an application.
     *
     *  The rustsecp256k1_v0_4_0_ecdsa_sign function will by default create signatures in the
     *  lower-S form, and rustsecp256k1_v0_4_0_ecdsa_verify will not accept others. In case
     *  signatures come from a system that cannot enforce this property,
     *  rustsecp256k1_v0_4_0_ecdsa_signature_normalize must be called before verification.
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ecdsa_signature_normalize(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_ecdsa_signature* sigout,
        const rustsecp256k1_v0_4_0_ecdsa_signature* sigin
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(3);

    /** An implementation of RFC6979 (using HMAC-SHA256) as nonce generation function.
     * If a data pointer is passed, it is assumed to be a pointer to 32 bytes of
     * extra entropy.
     */
    SECP256K1_API extern const rustsecp256k1_v0_4_0_nonce_function rustsecp256k1_v0_4_0_nonce_function_rfc6979;

    /** A default safe nonce generation function (currently equal to rustsecp256k1_v0_4_0_nonce_function_rfc6979). */
    SECP256K1_API extern const rustsecp256k1_v0_4_0_nonce_function rustsecp256k1_v0_4_0_nonce_function_default;

    /** Create an ECDSA signature.
     *
     *  Returns: 1: signature created
     *           0: the nonce generation function failed, or the secret key was invalid.
     *  Args:    ctx:       pointer to a context object, initialized for signing (cannot be NULL)
     *  Out:     sig:       pointer to an array where the signature will be placed (cannot be NULL)
     *  In:      msghash32: the 32-byte message hash being signed (cannot be NULL)
     *           seckey:    pointer to a 32-byte secret key (cannot be NULL)
     *           noncefp:   pointer to a nonce generation function. If NULL, rustsecp256k1_v0_4_0_nonce_function_default is used
     *           ndata:     pointer to arbitrary data used by the nonce generation function (can be NULL)
     *
     * The created signature is always in lower-S form. See
     * rustsecp256k1_v0_4_0_ecdsa_signature_normalize for more details.
     */
    SECP256K1_API int rustsecp256k1_v0_4_0_ecdsa_sign(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_ecdsa_signature* sig,
        const unsigned char* msghash32,
        const unsigned char* seckey,
        rustsecp256k1_v0_4_0_nonce_function noncefp,
        const void* ndata
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

    /** Verify an ECDSA secret key.
     *
     *  A secret key is valid if it is not 0 and less than the secp256k1 curve order
     *  when interpreted as an integer (most significant byte first). The
     *  probability of choosing a 32-byte string uniformly at random which is an
     *  invalid secret key is negligible.
     *
     *  Returns: 1: secret key is valid
     *           0: secret key is invalid
     *  Args:    ctx: pointer to a context object (cannot be NULL)
     *  In:      seckey: pointer to a 32-byte secret key (cannot be NULL)
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_seckey_verify(
        const rustsecp256k1_v0_4_0_context* ctx,
        const unsigned char* seckey
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);

    /** Compute the public key for a secret key.
     *
     *  Returns: 1: secret was valid, public key stores
     *           0: secret was invalid, try again
     *  Args:   ctx:        pointer to a context object, initialized for signing (cannot be NULL)
     *  Out:    pubkey:     pointer to the created public key (cannot be NULL)
     *  In:     seckey:     pointer to a 32-byte secret key (cannot be NULL)
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_pubkey_create(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_pubkey* pubkey,
        const unsigned char* seckey
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Negates a secret key in place.
     *
     *  Returns: 0 if the given secret key is invalid according to
     *           rustsecp256k1_v0_4_0_ec_seckey_verify. 1 otherwise
     *  Args:   ctx:    pointer to a context object
     *  In/Out: seckey: pointer to the 32-byte secret key to be negated. If the
     *                  secret key is invalid according to
     *                  rustsecp256k1_v0_4_0_ec_seckey_verify, this function returns 0 and
     *                  seckey will be set to some unspecified value. (cannot be
     *                  NULL)
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_seckey_negate(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* seckey
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);

    /** Same as rustsecp256k1_v0_4_0_ec_seckey_negate, but DEPRECATED. Will be removed in
     *  future versions. */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_privkey_negate(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* seckey
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);

    /** Negates a public key in place.
     *
     *  Returns: 1 always
     *  Args:   ctx:        pointer to a context object
     *  In/Out: pubkey:     pointer to the public key to be negated (cannot be NULL)
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_pubkey_negate(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_pubkey* pubkey
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);

    /** Tweak a secret key by adding tweak to it.
     *
     *  Returns: 0 if the arguments are invalid or the resulting secret key would be
     *           invalid (only when the tweak is the negation of the secret key). 1
     *           otherwise.
     *  Args:    ctx:   pointer to a context object (cannot be NULL).
     *  In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
     *                  invalid according to rustsecp256k1_v0_4_0_ec_seckey_verify, this
     *                  function returns 0. seckey will be set to some unspecified
     *                  value if this function returns 0. (cannot be NULL)
     *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
     *                  rustsecp256k1_v0_4_0_ec_seckey_verify, this function returns 0. For
     *                  uniformly random 32-byte arrays the chance of being invalid
     *                  is negligible (around 1 in 2^128) (cannot be NULL).
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_seckey_tweak_add(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* seckey,
        const unsigned char* tweak32
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Same as rustsecp256k1_v0_4_0_ec_seckey_tweak_add, but DEPRECATED. Will be removed in
     *  future versions. */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_privkey_tweak_add(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* seckey,
        const unsigned char* tweak32
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Tweak a public key by adding tweak times the generator to it.
     *
     *  Returns: 0 if the arguments are invalid or the resulting public key would be
     *           invalid (only when the tweak is the negation of the corresponding
     *           secret key). 1 otherwise.
     *  Args:    ctx:   pointer to a context object initialized for validation
     *                  (cannot be NULL).
     *  In/Out: pubkey: pointer to a public key object. pubkey will be set to an
     *                  invalid value if this function returns 0 (cannot be NULL).
     *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
     *                  rustsecp256k1_v0_4_0_ec_seckey_verify, this function returns 0. For
     *                  uniformly random 32-byte arrays the chance of being invalid
     *                  is negligible (around 1 in 2^128) (cannot be NULL).
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_pubkey_tweak_add(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_pubkey* pubkey,
        const unsigned char* tweak32
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Tweak a secret key by multiplying it by a tweak.
     *
     *  Returns: 0 if the arguments are invalid. 1 otherwise.
     *  Args:   ctx:    pointer to a context object (cannot be NULL).
     *  In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
     *                  invalid according to rustsecp256k1_v0_4_0_ec_seckey_verify, this
     *                  function returns 0. seckey will be set to some unspecified
     *                  value if this function returns 0. (cannot be NULL)
     *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
     *                  rustsecp256k1_v0_4_0_ec_seckey_verify, this function returns 0. For
     *                  uniformly random 32-byte arrays the chance of being invalid
     *                  is negligible (around 1 in 2^128) (cannot be NULL).
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_seckey_tweak_mul(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* seckey,
        const unsigned char* tweak32
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Same as rustsecp256k1_v0_4_0_ec_seckey_tweak_mul, but DEPRECATED. Will be removed in
     *  future versions. */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_privkey_tweak_mul(
        const rustsecp256k1_v0_4_0_context* ctx,
        unsigned char* seckey,
        const unsigned char* tweak32
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Tweak a public key by multiplying it by a tweak value.
     *
     *  Returns: 0 if the arguments are invalid. 1 otherwise.
     *  Args:    ctx:   pointer to a context object initialized for validation
     *                  (cannot be NULL).
     *  In/Out: pubkey: pointer to a public key object. pubkey will be set to an
     *                  invalid value if this function returns 0 (cannot be NULL).
     *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
     *                  rustsecp256k1_v0_4_0_ec_seckey_verify, this function returns 0. For
     *                  uniformly random 32-byte arrays the chance of being invalid
     *                  is negligible (around 1 in 2^128) (cannot be NULL).
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_pubkey_tweak_mul(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_pubkey* pubkey,
        const unsigned char* tweak32
    ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

    /** Updates the context randomization to protect against side-channel leakage.
     *  Returns: 1: randomization successfully updated or nothing to randomize
     *           0: error
     *  Args:    ctx:       pointer to a context object (cannot be NULL)
     *  In:      seed32:    pointer to a 32-byte random seed (NULL resets to initial state)
     *
     * While secp256k1 code is written to be constant-time no matter what secret
     * values are, it's possible that a future compiler may output code which isn't,
     * and also that the CPU may not emit the same radio frequencies or draw the same
     * amount power for all values.
     *
     * This function provides a seed which is combined into the blinding value: that
     * blinding value is added before each multiplication (and removed afterwards) so
     * that it does not affect function results, but shields against attacks which
     * rely on any input-dependent behaviour.
     *
     * This function has currently an effect only on contexts initialized for signing
     * because randomization is currently used only for signing. However, this is not
     * guaranteed and may change in the future. It is safe to call this function on
     * contexts not initialized for signing; then it will have no effect and return 1.
     *
     * You should call this after rustsecp256k1_v0_4_0_context_create or
     * rustsecp256k1_v0_4_0_context_clone (and rustsecp256k1_v0_4_0_context_preallocated_create or
     * rustsecp256k1_v0_4_0_context_clone, resp.), and you may call this repeatedly afterwards.
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_context_randomize(
        rustsecp256k1_v0_4_0_context* ctx,
        const unsigned char* seed32
    ) SECP256K1_ARG_NONNULL(1);

    /** Add a number of public keys together.
     *
     *  Returns: 1: the sum of the public keys is valid.
     *           0: the sum of the public keys is not valid.
     *  Args:   ctx:        pointer to a context object
     *  Out:    out:        pointer to a public key object for placing the resulting public key
     *                      (cannot be NULL)
     *  In:     ins:        pointer to array of pointers to public keys (cannot be NULL)
     *          n:          the number of public keys to add together (must be at least 1)
     */
    SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int rustsecp256k1_v0_4_0_ec_pubkey_combine(
        const rustsecp256k1_v0_4_0_context* ctx,
        rustsecp256k1_v0_4_0_pubkey* out,
        const rustsecp256k1_v0_4_0_pubkey* const* ins,
        size_t n
    ) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

#ifdef __cplusplus
}
#endif

#endif /* SECP256K1_H */
